1. Field of the Invention
The present invention relates to a plasma etching system, and more particularly, relates to a plasma etching system having magnets in an electrode facing a substrate holder so as to control the magnetic field strength in the space in front of the substrate and thereby enabling various types of substrates to be etched and improving the etch rate.
2. Description of the Related Art
First an example of a plasma etching system of the related art will be explained with reference to FIG. 6. The plasma etching system is provided with a vacuum chamber 100. At the center of the ceiling 101 of the vacuum chamber 100 a disk-shaped electrode 103 is arranged through a ring-shaped insulator 102. At the bottom 104 of the vacuum chamber 100 a substrate holder 106 is arranged on a ring-shaped insulator 105. The electrode 103 and the substrate holder 106 are placed facing each other in a parallel state. Each of the electrode 103 and the substrate holder 106 has a built-in known mechanism for controlling the temperature. Further, the electrode 103 and the substrate holder 106 are connected to power sources 107 and 108 respectively. Electric power for inducing the discharge is supplied between the electrode 103 and the substrate holder 106 by these power sources 107 and 108. An evacuation port 110 is provided at the surrounding side wall 109 of the vacuum chamber 100. The evacuation port 110 has connected to it an evacuating mechanism 112 through a pressure control valve 111. A cylindrical shield member 113 is arranged at the inside of the surrounding side wall 110 around the substrate holder 106. Plasma is produced in the space inside the shield member 113. In the space the plasma performs an etching process. The shield member 113 is formed with several holes 113a. The inside and the outside of the shield member 113 are connected through these holes. The shield member 113 prevents contamination of the inner surface of the vacuum chamber 100. The electrode 103 is provided with a gas introduction mechanism for introducing process gas. The gas inlet mechanism is comprised of a gas distribution plate 114 and a gas blowoff plate 115. The gas introduction mechanism is connected to a gas supply source (not shown) through a gas introduction pipe 116 from the side of the upper surface of the electrode 103. The gas blowoff plate 115 has a large number of gas blowoff holes 115a. The process gas is introduced in the space in front of the substrate holder 106 through these gas blowoff holes. The member 117 provided at the substrate holder 106 is a pushout rod for carrying the substrates 118.
In the above configuration, a substrate 118 carried by a not shown substrate carrying mechanism is loaded on the substrate holder 106. Process gas is introduced into the vacuum chamber 100 through the gas introduction pipe 116. The process gas passes through the gas distribution plate 115 and the gas blowoff plate 114 provided at the bottom side of the electrode 103 and is introduced into the vacuum chamber 100. On the other hand, the evacuating mechanism 112 evacuates the internal space 100A of the vacuum chamber 100 to create a required vacuum state. The internal pressure of the shield member 113 is controlled to a suitable pressure by the pressure control valve 111. The internal pressure of the shield member 113 is determined in accordance with the process. Next, the electric power is fed between the substrate holder 106 and the electrode 103 by the power sources 107 and 108 to cause a discharge in the space (space above substrate in internal space 100A) in front of the substrate 106 to generate plasma. This plasma is utilized for etching a material to be etched on the substrate 118. At this time, the process gas introduced into the inside region of the shield member 113 is equally blown off over the substrate 118 by the gas distribution plate 114 and the gas blowoff plate 115 provided in the vacuum at the electrode 103.
In the configuration of the plasma etching system of the related art, the factors causing changes in the etch rate or etching distribution of the etched material on the surface of the substrate 118 are mainly the internal pressure of the vacuum chamber, the process gas, the fed electric power, and other process conditions. Therefore, conversely, when changing these process conditions, it is possible to change the etch rate or etching distribution of the etched material. Even if the process conditions are changed so as to improve the etch rate or etching distribution by a large extent, in practice, it is difficult to set process conditions to achieve a major improvement. Further, by changing the hardware configuration of a plasma etching system (for example, expanding or reducing the discharge region by modification of the shape of the shield member, or modification of the shape of the substrate holder), it is possible to control the etch rate or etching distribution of the etched material. In this case, however, it is necessary to remodel the system by a large extent in accordance with various processes. This becomes a large problem in terms of costs and the trouble in work.
An object of the present invention is to provide a plasma etching system which enables the establishment of a better etching process for various etched materials by just the use of magnets and further improvement of the magnets, enables various demands from end users to be met, and enables improvement of the speed of process development.
The plasma etching system according to the present invention is configured as follows to achieve the above object.
The plasma etching system according to the present invention has as a basic configuration a vacuum chamber functioning as a plasma etching chamber and a substrate holder and an electrode arranged facing each other in the inside of the vacuum chamber. A substrate is loaded on the substrate holder. The electrode has a mechanism for introducing a process gas and a gas blowoff plate. The inside of the vacuum chamber is evacuated by an evacuating mechanism and held at a predetermined reduced pressure state or vacuum state. In the state with the substrate loaded on the substrate holder, process gas is introduced inside the vacuum chamber and power is fed between the substrate holder and the electrode to generate plasma. This plasma etches the surface of the substrate. In this configuration, further, a plurality of ring-shaped magnets are arranged at concentric positions at the inside of the vacuum chamber at the rear side of the gas blowoff plate arranged at the electrode. These magnets are arranged so that the poles at the inside surfaces alternate in polarity. The magnetic field strength resulting from the plurality of magnets on the surface of the substrate is made substantially 0 Gauss.
According to the above plasma etching system, the plasma is controlled by providing magnets serving also as a gas distribution plate right behind (or right in front of) the gas blowoff plate so as to create a required distribution of magnetic field and magnetic field strength at the region where the plasma is produced. Due to this, it becomes possible to improve the distribution of the etched material on the substrate and improve the etch rate. By making the magnetic field strength near the surface of the substrate substantially 0, the damage to the substrate is reduced.
In the above configuration, preferably, the magnetic field strength resulting from the plurality of magnets at a plane positioned substantially at the center of the substrate holder and the electrode is made a uniform one of about 100 Gauss. By setting the distribution of the magnetic field resulting from the magnets to the value of the magnetic field strength explained above at the above center position, the above effects are effectively manifested.
In the plasma etching system having the above configuration, preferably, the magnetic field strength resulting from the plurality of magnets at the plane positioned substantially at the center of the substrate holder and the electrode is made a uniform one of about 200 Gauss. A similar effect can be exhibited even if setting the value of the magnetic field strength at the above center position at the above value.
In the plasma etching system having the above configuration, preferably, a plurality of magnets are fixed to a gas distribution plate and gas introduction holes are formed in the gas distribution plate corresponding to the intervals between the two included in the plurality of magnets. The gas distribution plate has a plurality of gas introduction holes for introducing into the vacuum chamber a process gas creating the etching gas. These gas introduction holes are formed using the locations corresponding to the spaces between the plurality of magnets since the plurality of ring-shaped magnets are fixed to the gas distribution plate arranged concentrically. Due to the actions of the plurality of ring-shaped magnets arranged in the concentric positional relationship and the gas distribution plate, a gas distribution function causing distribution of the introduced gas is realized.
In the plasma etching system according to the present invention, since a plurality of ring-shaped magnets are provided concentrically in a predetermined positional relationship at a position right behind the gas blowoff plate positioned above the substrate holder, the magnets are arranged so that their inside polar surfaces become alternately S and N, and the magnets are set so as to enable the magnetic field strength at the plane near the substrate surface and the magnetic field strength at a plane at the above center position to be set to predetermined values, the etch rate and etching distribution of the etched material can be greatly improved and the damage to the substrate can be minimized. Further, since the spread of the discharge is suppressed, the power can be concentrated and high efficiency and energy savings can be realized.